1. Field of Invention
The present invention relates a variable valve lift device, and more particularly to a continuous variable valve lift device in which two intake valves are operated to have valve lift values different from each other in a low load operation range of an engine for enhancing flowability of intake introduced to a combustion chamber through the two intake valves to improve fuel consumption of the engine.
2. Description of Related Art
In general, the engine of a vehicle is provided with the combustion chamber for burning the fuel to generate power, and a valve train having intake valves each for controlling inflow of air or a mixture of the air and the fuel into the combustion chamber and exhaust valves each for controlling outflow of exhaust gas generated as the fuel burns from the combustion chamber.
And, as the intake and exhaust valves in the valve train are operated by cams interlocked with rotation of a crankshaft which is rotated by power generated by combustion of the fuel, the intake/exhaust valves opens/closes the combustion chamber, respectively.
If the cams have fixed profiles making the intake/exhaust valves to have fixed lift values respectively too, flow rates of the inflow/the outflow of the air and exhaust gas through the intake/exhaust valves are also fixedly set according to the lift values of the cams, respectively.
In the meantime, if the lift values of the intake/exhaust valves are controlled according to an operation state of the engine of the vehicle, appropriately, fuel consumption can be improved and an output of the engine can be increased. Accordingly, a variable valve lift device is suggested for controlling the lift values of the intake/exhaust valves according to the operation state of the engine.
Of the variable valve lift devices, a continuous variable valve lift device (CVVL) can devise the improvement of the fuel consumption as well as the increase of the output of the engine if the lift values of the valves are controlled within a range of 1 mm to 11 mm appropriately according on an operation range of the engine.
Of the continuous variable valve lift devices, so called an unequal continuous variable valve lift device is also disclosed in which, when the engine having the two intake valves is operated in a low load, if the two intake valves are controlled such that the valve lift values of the two intake valves are different from each other for enhancing flowability of the intake introduced to the combustion chamber through the two intake valves, thereby improving the fuel consumption of the engine.
On the unequal continuous variable valve lift devices, an unequal continuous variable valve lift structure is required, which can simplify a structure thereof and improve operation reliability.
The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.